1. Field of the Invention
This invention relates generally to the field of treating wells to stimulate fluid production. More particularly, the invention relates to the field of high pressure abrasive fluid injection in oil and gas wells.
2. Description of the Related Art
Abrasive jet perforating uses fluid slurry pumped under high pressure to perforate tubular goods around a wellbore, where the tubular goods include tubing, casing, and cement. Since sand is the most common abrasive used, this technique is also known as sand jet perforating (SJP). Abrasive jet perforating was originally used to extend a cavity into the surrounding reservoir to stimulate fluid production. It was soon discovered, however, that abrasive jet perforating could not only perforate, but cut (completely sever) the tubular goods into two pieces. Sand laden fluids were first used to cut well casing in 1939. Abrasive jet perforating was eventually attempted on a commercial scale in the 1960s. While abrasive jet perforating was a technical success (over 5,000 wells were treated), it was not an economic success. The tool life in abrasive jet perforating was measured in only minutes and fluid pressures high enough to cut casing were difficult to maintain with pumps available at the time. A competing technology, explosive shape charge perforators, emerged at this time and offered less expensive perforating options.
Consequently, very little work was performed with abrasive jet perforating technology until the late 1990's. Then, more abrasive-resistant materials used in the construction of the perforating tools and jet orifices provided longer tool life, measured in hours or days instead of minutes. Also, advancements in pump materials and technology enabled pumps to handle the abrasive fluids under high pressures for longer periods of time. The combination of these advances made the abrasive jet perforating process more cost effective. Additionally, the recent use of coiled tubing to convey the abrasive jet perforating tool down a wellbore has led to reduced run time at greater depth. Further, abrasive jet perforating did not require explosives and thus avoids the accompanying danger involved in the storage, transport, and use of explosives. However, the basic design of abrasive jet perforating tools used today has not changed significantly from those used in the 1960's.
Abrasive jet perforating tools and casing cutters were initially designed and built in the 1960's. There were many variables involved in the design of these tools. Some tool designs varied the number of jet locations on the tool body, from as few as two jets to as many as 12 jets. The tool designs also varied the placement of those jets, such, for example, positioning two opposing jets spaced 180° apart on the same horizontal plane, three jets spaced 120° apart on the same horizontal plane, or three jets offset vertically by 30°. Other tool designs manipulated the jet by orienting it at an angle other than perpendicular to the casing or by allowing the jet to move toward the casing when fluid pressure was applied to the tool.
The following publications are representative of conventional abrasive jet perforating and cutting tools, along with apparatuses and methods that may be employed with the tools.
An SPE publication by J. S. Cobbett, “Sand Jet Perforating Revisited”, SPE 55044, SPE Drill. & Completion, Vol. 14, No. 1, p. 28-33, March 1999, discloses the use of sand jet perforating (abrasive jet perforating) with coiled tubing to increase production in damaged wells, using examples of neglected wells in Lithuania.
A publication by Gensheng Li et al., “Abrasive Water Jet Perforation—An Alternative Approach to Enhance Oil Production”, Petroleum Science and Technology, Vol. 22, Nos. 5 & 6, p. 491-504, 2004, discloses laboratory results and field tests showing the effects of different parameters on the ability of abrasive water jet perforating (abrasive jet perforating) to improve well performance and the mechanism by which it works.
A new way to incorporate abrasive fluid or slurry into a high pressure fluid stream has been needed for many years. However, recent demands for certain oilfield technology have increased that need. Currently, large fracturing pumps or cementing pumps are used to pump the abrasive fluid to sand jet perforating tools. A polymer or gel is added to the carrier fluid (usually water) and then the abrasive is either mixed in batch or added “on the fly” through a mechanical feeder into the fluid stream at high volume, but low pressure. The low pressure allows techniques like Venturi mixers (such as mud mixers or water jet eductors) to be used to incorporate the abrasive into the fluid. These low pressure techniques do not work for mixing at the high pressures produced by pumps that operate from 2,000 psi to 10,000 psi, since the pressure differential is too great. After the slurry is mixed at low pressure, it is then fed to the abrasive high pressure pump unit. These pumps have valves, plungers and other parts that are made of materials able to withstand the eroding action of the abrasive fluid at high pressure. The fluid slurry is then pumped at high pressure downhole to the abrasive jet tool.
Other industries (such as high pressure water blasting) that use abrasives on the surface with high pressure for cleaning and cutting, currently add the abrasive in front of the fluid stream. This process keeps the abrasive from contact with the high pressure equipment. However, the abrasive is not as effective when added to the high pressure fluid stream at the end as when the sand is already entrained in the fluid. The sand particles do not have time to reach full velocity before they encounter the target material.
Thus, a need exists for a system and a method for more efficiently and more inexpensively injecting an abrasive fluid mixture into a high pressure fluid flow for use in an abrasive jet tool.